1. Field of the Invention
The present invention relates to a switching mechanism, particularly a sensing edge for a powered movable door, and more particularly to a switching mechanism for stopping or reversing the movement of a closing door upon contact with an object in the path of the door.
2. Background of the Art
Sensing edge switches for movable doors are known. For example, U.S. Pat. No. 5,072,079 to Miller discloses a sensing edge for a door which includes a first sheet of electrically conductive material, a layer of non-conductive material, a second sheet of electrically conductive material, a second sheet of resiliently compressible material and an elongate inner core having a predetermined elastic compressibility.
U.S. Pat. No. 4,051,336 to Miller discloses a pressure sensitive door edge construction including a channel facing outwardly from a door and having in-turned lips defining a slot therebetween, a resiliently depressible bead extending exteriorly along the channel bridging the slot, a reduced neck on the inner side of the bead extending through the slot, an inner enlargement on the neck interiorly of the channel, and pressure responsive means operatively connected to the bead for stopping door movement upon bead depression.
Both these and other safety edges operate by a switch closing operation. That is, the safety edges include two or more electrode strips which are spaced apart from each other. When an object is encountered by the safety edge during the closing of the door, one electrode strip is moved into contact with the other to close the switch, i.e., to move the switch into the xe2x80x9conxe2x80x9d configuration to complete the electric circuit and allow current to flow. This operation typically powers a signal for reversing or stopping the motion of the door.
Such xe2x80x9cnormally openxe2x80x9d door edge safety switches suffer from certain disadvantages. For example, monitoring the working condition of such switches usually requires a special signal conditioner, or a four wire system. Moreover, the molded rubber cover used in door edge safety switches usually has disparities of shape over its length. Inconsistencies in thickness of the rubber, for example, can keep the electrode strips permanently in contact at some point along the length of the strips, especially in sensitive switches wherein the electrode strips are positioned close together. What is needed is a simplified safety edge switch for a door wherein the sensitivity is not limited by the disparities in the rubber cover. These and other advantages are realized in the safety edge switch described herein.
A safety edge switch for a movable door is provided herein. The safety edge switch includes: a base; a first resiliently deformable material; an electrode array which includes a plurality of segments of a first conductive material, each segment being separated from neighboring segments by respective gaps, the electrode array being in a fixed position relative to the base; and, a second array which includes a plurality of spaced apart electrically conductive bridging members, the second array being movable in response to deformation of the first resiliently deformable material from a closed circuit first position wherein the bridging members are each in contact with respective segments of the first conductive material so as to bridge a respective gap between said respective segments, and a force deformation second position wherein at least one of the bridging members is not in contact with at least one respective segment of the electrode array, wherein in the closed circuit position the segments of the electrode array are electrically connected in series so as to form an unbroken electrical path, and in the second position the electrical path is broken by at least one unbridged gap so as to form an open circuit.